A poor diet can damage the human body and cause conditions like kwashiorkor, scurvy, cardiovascular problems, diabetes, osteoporosis and metabolic syndrome. A healthy diet can prevent disease and ensure the proper functioning of an organism. Nutrition supplies the cells with the materials needed to sustain life. Dietitians are specialists trained to provide nutrition information and advice about meal planing, preparation and human nutrition. Clinical researchers investigate the role of nourishment in chronic disease and methods to alleviate or prevent a condition.
There are two types of diets: carnivore, with more nitrogen being consumed and herbivore, with higher carbon intakes. Chemicals such as carbohydrates, fatty acids, amino acids, nucleic acids and water can be found in the human body. They contain oxygen, hydrogen, nitrogen, carbon, magnesium, calcium, zinc and other compounds found various combinations like hormones, phospholipids and vitamins. The digestive juices break these chemicals bonds so they can pass into the bloodstream. Waste and unabsorbed products are eliminated from the body.
The main nutrient classes are vitamins, water, fats, carbohydrates, protein and minerals. Fats, carbohydrates, protein and water are macronutrients meaning they are needed in larger quantities. Minerals and vitamins are micronutrients along with antioxidants and phytochemicals. Macronutrients provide structural material while the latter protect and influence body systems. Too much of a certain nutrient or too little can cause death or illness.
The most comprehensive nutrition information can be found in the Dietary Reference Intakes (DRIs) created in 1997. The guidelines aim to reduce the risks of chronic diseases and to prevent deficiencies caused by a poor diet. DRI has four types of references: the Estimated Average Requirements, Recommended Dietary Allowances, Adequate Intakes and Tolerable Upper Limits. The dietary nutrition information was mainly used by registered dietitians and researchers but now it is available for anyone.
Calories are the main energy source for the body, but an excessive amount can lead to weight gain. Food and beverages contain calories that come from three essential nutrients: fat, carbohydrates and protein. One gram of carbohydrates contains four calories, one gram of fat nine calories and one gram of protein four calories. One gram of alcohol has nine calories. Calorie consumption has to be determined by gender, height, activity level, age and weight. Equations like Harris-Benedict and Mifflin-St. Jeor are used to calculate the number of maintenance calories a person needs. Going above or below the maintenance level by 3,500 calories will result in weight gain or lose. An extra 500 calories per day (3500 per week) will make a person gain 1 pound.